1. Field of the Invention
The present invention relates to a sheet processing apparatus for performing a processing such as bookbinding, punching, or stamping on sheets delivered from an image forming apparatus such as a copying machine or a printer; in particular, the present invention relates to a sheet processing apparatus in which multiple trays for accommodating sheet bundles are arranged in a limited space in an image forming apparatus and in which sheet bundles are stacked and accommodated on a tray selected through switching in accordance with the processing mode.
2. Description of the Related Art
A sheet processing apparatus includes a processing tray provided at the discharge port of an image forming apparatus such as a copying machine or a printer, and this processing tray is provided with processing apparatuses such as a stapling apparatus, a punching apparatus, and a stamping apparatus. Such a sheet processing apparatus, which performs processing on a series of sheets discharged from the image forming apparatus, is widely used as an apparatus for accommodating processed sheets on an accumulating tray on the downstream side. Recently, there has been proposed an apparatus which, when accommodating sheets on an accommodating tray by the processing apparatus, folds the sheets into a booklet.
As a conventional apparatus for folding sheets into a booklet when accommodating the sheets, there is known a processing apparatus installed on the downstream side of an image forming apparatus, the processing apparatus including a first tray accommodating sheets discharged from the image forming apparatus without performing any processing thereon, and a second tray which accommodates processed sheets (bundle) in a folded state (see, for example, Japanese Patent Application Laid-Open No. H11-11783). In the sheet processing apparatus disclosed in the above-mentioned publication, switching is selectively effected between a first tray and a second tray serving as discharge trays. The selected discharge tray is vertically moved, and is matched with a processing tray arranged on the upstream side.
When folding a sheet bundle that has undergone binding processing on a tray, the sheets aligned and accumulated on the processing tray are conventionally folded by a sheet folding mechanism, with the sheets being dropped for accommodation from a discharge port arranged above the tray, as disclosed in Japanese Patent Application Laid-Open No. H11-11783. That is, a discharge port is provided above the tray, and the sheets are caused to fall from the discharge port starting with the folded ends thereof to be further stacked on sheets that have already been stacked.
As another example of a sheet processing apparatus, there is known a layout construction in which a discharge port is arranged above an image forming unit, with an image reading unit being arranged further above (see, for example, Japanese Patent Application Laid-Open No. 2006-248686). In this disclosed example, a processing unit for performing stapling on accumulated sheet bundles is arranged at the discharge port between the image forming unit and the image reading unit.
In the unit construction of the sheet processing apparatus disclosed in Japanese Patent Application Laid-Open No. H11-11783, the apparatus housings of the image forming apparatus and the sheet processing apparatus are successively arranged so as to be adjacent to each other. Thus, a large installation space is required, resulting in an increase in the size of the system as a whole.
In view of this, in Japanese Patent Application Laid-Open No. 2006-248686, there is adopted a layout construction in which a processing unit is mounted in an image forming unit, thereby achieving a reduction in the system installation space.
However, in the construction disclosed in Japanese Patent Application Laid-Open No. H11-11783, an increase in the size of the system as a whole is involved as described above. Further, in the unit construction of Japanese Patent Application Laid-Open No. H11-11783, the stapling position where the sheets (sheet bundle) accumulated on the tray are bound together and the position of a folding blade (folding knife) for folding the sheet bundle are the same. Therefore, the layout construction of the two apparatuses are rather complicated, which leads to a rather difficult apparatus assembling operation at the time of production and a problem in terms of product reliability.
In view of this, by adopting a layout construction in which the processing unit is mounted on the image forming unit, it might be possible to perform binding (stapling) on the center of a sheet bundle, folding the sheet bundle, and accommodating the sheet bundle on the discharge tray in a folded state. In this layout, however, the accommodation of processed sheets, that is, the discharge/accommodation of stapled sheets, discharge/accommodation of folded sheets, discharge/accommodation of unprocessed sheets, and the sheet discharge mechanism are rather complicated.
Further, as disclosed in Japanese Patent Application Laid-open No. 11-11783, in the conventional sheet processing apparatus, the folded sheets stacked and accommodated on the tray are caused to fall onto sheets stacked on the tray for accommodation. Thus, it is necessary to arrange the discharge port and the sheet discharge route continuous therewith have to be arranged above the tray while forming a step, resulting in an increase in the size of the apparatus in the vertical direction. Thus, when arranging the tray unit in a limited space as in the case of the construction disclosed in Japanese Patent Application Laid-Open No. 2006-248686, there is involved a limitation in terms of space, and it is difficult to house the folding mechanism. Further, since the accommodation is effected through dropping, it is rather difficult to stack the sheets regularly on the tray.
Further, the folded sheets are accommodated such that their folded ends are directed forwardly in the discharging direction, with the discharge sheets being stacked on those sheets. Therefore, when the trailing ends of the stacked folded sheets are open (diverged), the leading ends in the discharging direction of the sheets to be discharged next are allowed to touch the trailing ends, which means there is a risk of the sheet attitude being disturbed. Further, in the case of the layout in which the tray is arranged above the folding route, the processing route, and then the tray are arranged successively in the sheet discharging direction, resulting in an increase in the size of the apparatus in the discharging direction and an increase in the installation space.
Further, as described above, in the construction disclosed in Japanese Patent Application Laid-Open No. H11-11783, the processing apparatus is arranged on the downstream side of the image forming apparatus so as to be adjacent thereto. This processing apparatus has a processing tray for first aligning and accumulating sheets, and a folding mechanism for folding the aligned sheet bundle in a bound state is arranged on the downstream side of this processing tray. Further, a tray unit for accommodating the sheets is arranged on the downstream side of the folding mechanism, and hence an increase in the size of the apparatus is involved.
Further, in the conventional apparatus, the sheet (bundle) folded by the folding mechanism is conveyed to the tray situated on the downstream side in the discharging direction, and hence the apparatus is rather large and requires a large installation space. In this way, conventionally, the folding mechanism is arranged on the downstream side of the processing tray for aligning the sheets, and the sheet bundle is conveyed from this folding mechanism to the tray situated on the downstream side in the discharging direction, and hence an increase in apparatus size is inevitable.